U.S. President Barack Obama on Tuesday said Russia and China understood the dangers of a Syrian civil war but had not yet "signed on" to a plan to prod President Bashar Assad from power.

Obama said after meeting Presidents Vladimir Putin and Hu Jintao at the G20 summit in Mexico that he hoped work could take place on a political transition plan to present to the Syrian people in the next two weeks.

The United Nations is to keep unarmed monitors in Syria despite the escalation of hostilities which led to the suspension of patrols, top U.N. officials said Tuesday.

Major General Robert Mood, head of the U.N. Supervision Mission in Syria (UNSMIS), told the U.N. Security Council the nearly 300 monitors were "morally obliged" to stay despite facing intensive attacks, diplomats said.

The United States on Tuesday added Syria to a blacklist of countries failing to abide by conventions barring human trafficking and slavery, a move which leads to sanctions and cuts in U.S. aid.

"The government of Syria does not fully comply with the minimum standards for the elimination of trafficking and is not making significant efforts to do so," the 2012 Trafficking in Persons report said.

Scores of "gullible" Filipinos are being tricked into going to work in Syria each month despite an official ban on travel to the violence-wracked country, the Philippine government said Tuesday.

The Filipinos, mostly women who go and work as maids, are being duped into working in Syria with false promises of high salaries and assurances that they will be safe, Labor Department spokesman Nicon Fameronag told Agence France Presse.

United Nations Secretary General Ban Ki-moon is "gravely concerned" about the rising death toll in Syria, a top official said Tuesday ahead of a U.N. Security Council meeting on the escalating conflict.

Ban wants the Security Council to unite to apply "sustained pressure" on Syrian government to apply the peace plan of U.N.-Arab League envoy Kofi Annan, assistant secretary general Oscar Fernandez Taranco told the 15-nation body.

Jordan has tightened border controls to prevent loyalists of Syrian President Bashar al-Assad from infiltrating into the kingdom, an official of the opposition Syrian National Council said on Tuesday.

"Jordan used to have an open border policy with the Syrians, but now new regulations prevent some Syrians from entering the kingdom," Amman-based SNC official Nizar Heraki told Agence France Presse.

Troops pounded and raided rebel strongholds across Syria and clashes erupted in Homs on Tuesday as 36 people were killed in violence nationwide, a watchdog said.

Regime forces clashed with rebels before dawn in Homs where a soldier was killed amid "intermittent shelling" of the central city, said the Syrian Observatory for Human Rights.

The Free Syrian Army Tuesday called on their "Kurdish brothers" to join rebels fighting President Bashar Assad's regime, while promising an end to injtices against Kurds in a future democratic Syria.

"The Joint Command of the Free Syrian Army ... appeals to our Kurdish brothers, soldiers and civilians, and invites them to join the ranks of the FSA inside the country," the group's spokesman Colonel Kassem Saadeddine said in an online video.

Syria on Tuesday accused gunmen of using Homs residents as "human shields" and of blocking government's efforts to evacuate them from the besieged central city.

"Contacts have been made with the head of the U.N. observers and local authorities in order to facilitate the departure of innocent citizens (besieged) in Homs," the foreign ministry said in a statement.

A Russian ship allegedly carrying attack helicopters and missiles destined for Syria has stopped off the Scottish coast after its British insurer withdrew cover for the vessel.

Britain said it was aware of a consignment of refurbished Russian-made helicopters on a ship heading to Syria but did not specify the vessel, and refused to confirm reports that it had alerted the insurer.